Back to Work: The Controller, MOSFETs and the Curtis 1204

OK, go back to the Corbin Quicksilver bike. Mike was running a series of contactors handling this gawd-awful amount of current and voltage, which, after he described it to me I said, “holy shit”, to which he responded, “…that’s what I said”. It was 1972. My question is simple – why weren’t we using a speed controller?

In around 1954, a guy named Georg Sichling filed a patent for what seems like the first motor control using transistors and pulses of power. In the late ’50s you see a few similar patents, and then again in the ’70s, so, the question remains, why didn’t Mike use this type of motor control then? The answer to that question is in the description of the patent behind the Curtis 1204 controller -US4626750A, dated 1985 – arguably the DC speed controller that changed the game in the golf cart and forklift sectors:

Recent control systems for battery powered d.c. traction motors have frequently employed silicon controlled rectifiers (SCRs) as “current chopper” control devices to provide a periodic on-off control to vary the current to the drive motor, and the resultant speed, by variation of the total average duration of “on” intervals. In this manner, the so-called duty cycle is adjusted. The SCR controls have been very satisfactory in many ways. However, they do have various problems including substantial cost, substantial energy losses, and substantial size and weight.

The fact is, controllers that were running anything like an EV’s current and voltage were enormous and expensive – one Baldor unit I heard described as about 300lbs, 4′ long and was rated at 300A. Along comes FETs – “field effect transistors”, then MOSFETs, then power MOSFETs, and finally IGBTs (Insulated Gate Bi-polar Transistors), and you have a significantly smaller device which is far more efficient, and, most importantly, can handle some huge power. The first papers proposing this came out in the early ’80s. By the late ’80s they went into production, and controllers like the Zilla and the DCP- the precursor to Alltrax.

Remember, also, the huge push of chip manufacturing that happened in the ’80s. It started with semiconductors, then, when Intel adopted the strategy of developing and manufacturing microprocessors (something that Japan wasn’t doing at that time) in an effort to leapfrog it’s larger semiconductor manufacturing over Japan’s, resulted in a perfect demonstration of Moore’s Law – prices started plummeting, and tech started growing exponentially.

Moore’s Law, remember, was at first speaking directly to transistor development, and “describes a driving force of technological and social change, productivity, and economic growth in the late twentieth and early twenty-first centuries.”

…and, apparently, motor controllers as well.

There’s an important point here that should not be left unmentioned. In a car, there were examples of SCR motor controllers being used in spite of their size and weight. In a motorcycle? The weight and space required simply made that kind of controller impossible to use. Once again, the motorcycle is the “killer ap” – the defining laboratory for testing the ultimate weight and size of EV drive systems.